Cryocoolers have become available, which may be utilized to create and maintain cryogenic environments locally. These technologies reduce or eliminate the need to transport cryogen from a production facility to the location where it is needed, greatly reducing the cost of transportation, logistic and cryogen storage formerly required at the local site.
For small systems requiring heat extraction of less than about 40 watts, flexible heat straps made of braided copper wires and the like are available to provide the thermal link between the cryogenic cooling station and the heat source. However, cryogenic cooling and maintaining cryogenic conditions (i.e., at a temperature below about 100° K) within relatively large cryogenic chambers (i.e., chambers which require heat extraction on the order of 40 W or more) is problematic.
Although high capacity cryocoolers are available from several commercial sources, a thermal link between the cold head of the cryocooler and the relatively large cryogenic chamber is not available and thermal links known in the art are incapable of providing the heat transfer necessary to maintain cryogenic conditions on larger systems. As the temperature of the cryogenic system is reduced, thermal contraction of the components results in mechanical strains being exerted on the cold station of the cryocooler. Typically, the rated mass-force which may be applied to the cold station of the cryocooler is on the order of 10 kg in any direction. Traditional heat straps capable of providing heat extraction of more than about 40 W at temperatures of about 100° K or below are short and bulky. The required dimensions of such heat straps exert relatively large forces on the cold station due to thermal contraction, causing it to fail.
Attempts to address these issues include employment of longer heat straps, which are inherently more flexible than their shorter counterparts. However, as length is added the thermal resistances increases in a predictable way. It has been discovered that heat straps having the required length to exert less than 10 kg of force on a cold head upon cooling to cryogenic temperatures are ineffective for use in heat extraction of more than 40 W under cryogenic conditions. In short, thermal straps which are short enough and large enough to handle the heat load are too rigid for heat transfer above 40 W at cryogenic temperatures, and thermal straps large enough to provide the flexibility necessary to reduce the force applied to the cold station upon cooling to cryogenic temperatures are unacceptable for use with heat loads of 40 W or more due to thermal resistance. There is a need for a flexible heat transfer system for use with on-site cryogenic coolers which is capable of transferring 40 W, 50 W, or more at cryogenic temperatures of 100° K or less without exerting damaging forces on the cooling station of the cryocooler.